Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one machine to delegate some of its work to another machine that might be, for example, better suited to perform that work.
The client computer (which could, for example, be a personal computer having the IBM OS/2 operating system installed thereon) has an application program running on its operating system ("IBM" and "OS/2" are trademarks of the International Business Machines Corporation). The application program will periodically require work to be performed on a server and/or data to be returned from a server for subsequent use by the application program. The server can be, for example, a high-powered mainframe computer running on IBM's MVS operating system. Client/server computing is not limited to the client being on one machine and the server being on another, and it is very common for both the client and server to be located on the same physical machine, with the client and server being separate processes running on the machine.
Oftentimes, in client/server computing systems, a client needs to maintain a record of some server-related information which the client will use in sending requests to a server. An example is in a security authentication process where a client must prove its identity to a trusted third-party control server before it is allowed to communicate directly with a working server which the client wishes to use to satisfy a request. The client must store a ticket which the client receives from the trusted control server and then provides to the working server during this authentication process. There is a need, in these types of systems, for the client to have the most recent version of the server-related data. Once the client obtains the server-related data in its internal store, the client keeps using this locally stored data in formulating further client requests. If a change is made to the server-related data and the client is not made aware of this change, the client will not be able to make a valid request to a server, as the client's locally stored server-related data is outdated.
One way of keeping the client's server-related data updated would be to treat the client as a server and send the client a request instructing the client to update its stored version of the data. However, this requires adding function to the client which makes the client system more complicated. It is more desirable to have a so-called "thin-client" which is purely a client and thus can only send requests and cannot receive requests from other distributed computers on the network.
Also, even if the client were provided with added function, it would still be necessary to keep track (at the server end) of which clients are concerned with which data so that a decision can be made as to which clients need to be notified of a data update. This requires much overhead at the server end. Further, as the number of client computers continues to increase, there are more and more clients to send update requests to. Thus, it becomes difficult to scale up a network to include a larger number of clients.